To the gate of a power semiconductor element, such as an IGBT (insulated-gate bipolar transistor), which switches a high current, a high voltage of 10 V or higher has to be applied. Thus, the gate of the power semiconductor element is often driven by a high-voltage high-side MOS transistor and a low-side MOS transistor.
The source of the high-side MOS transistor is connected to the gate of the power semiconductor element via a resistor, and the drain of the low-side MOS transistor is also connected to the gate of the power semiconductor element via a resistor.
However, if some defects cause the drain of the high-side MOS transistor to short out at a ground level (ground fault) or the drain of the low-side MOS transistor to short out at a power supply level (supply fault), a large current flows between the source and the drain of the short-circuited high-side MOS transistor or low-side MOS transistor and a breakdown occurs.